Snakes are found all over the world except in the Arctic, New
Zealand and Ireland, and are more commonly distributed in temperate and
tropical countries. (1) Snakes are most likely to bite human beings when
they feel threatened, startled or provoked, and/or have no means of
escape when cornered. Snakes are likely to approach residential areas
when attracted by prey, such as mice and frogs. The Deccan plateau, with
its agricultural land and hot, dry climate, provides an ideal
environment for cobras, kraits and vipers. (2) Snakebite is generally
considered to be a rural problem and has been linked with environmental
and occupational conditions. (3) Most houses in the rural areas of India
are made of mud and have many crevices where rodents flourish. Snakes
have easy ingress to such houses and often enter them in search of food.
Firewood and dried cow dung, stored in or near the house, provide ready
shelter for snakes and rodents. (4)

Morbidity and mortality from snakebite envenomation depends on the
species of snake, since the estimated fatal dose of venom varies among
species. In India, almost two-thirds of the bites are attributed to the
saw-scaled viper (as high as 95% in some areas such as Jammu (5)), about
a quarter to Russell's viper, and smaller proportions to cobras and
kraits. (6)

Snakebite is an important and serious medical problem in many parts
of India. However, reliable data for morbidity and mortality are not
available since there is no proper reporting system. Moreover, many
cases are not recorded in official statistics, as people seek
traditional treatment methods. Most snakebite studies in India deal with
clinical and management aspects, and there are few epidemiological
studies. (7) We studied the epidemiology of snakebite cases over a
period of 10 years.

Aim and objectives

We aimed to study the epidemiology of snakebite cases admitted to
hospital; trends of snakebite and death from snakebite; seasonal
variations; and the outcomes of snakebite cases.

Methods

In a record-based retrospective descriptive study, we evaluated
snakebite cases admitted to the hospital from 1999 to 2008. Data were
collected from the Medical Records Department of the Dr Shankarrao
Chavan Government Medical College. Recorded information was entered in a
pre-coded pro forma and included age, sex, residence, site of bite, type
of snake poison, whether cases had been directly admitted to this
hospital or referred from other health centres, time interval between
snakebite and initiation of treatment, and the outcomes of snakebite
cases. The total number of hospital admissions for different illnesses
during 1999-2008 was 488 344. As required by the government of
Maharashtra, all snakebites are classified as medico-legal cases, whose
records are kept separately in the medical records department. The total
number of cases registered during the above period was 5 718. We
evaluated only the records of snakebite cases where outcomes were
recorded as recovered and discharged from hospital, or died while in
hospital. Excluded were snakebite patients who absconded or were
discharged against medical advice, and where records were incomplete. Of
the total of 5 718 snakebite cases, 179 records were not evaluated owing
to incomplete diagnosis, and patients absconded or discharged against
medical advice. Hence, 5 639 records of snakebite cases were evaluated.
The statistical tests applied were percentage and chi-square test,
wherever applicable.

Results

The age and sex distribution of the 5 639 cases studied is shown in
Table I. Snakebite was most common (57.7%) in the age group 31-45 years,
followed by the 16-30-year age group (27%), constituting a total of
84.7%. Males were more prevalent than females, the ratio being 2:1. Most
snake bites (3 115-55.2%) were seen during July-September, which
coincides with the rainy season in this region, followed by 1 210
(21.5%) cases during October-December. Fewer cases were seen in the
first and second quarters of the year--442 (7.8%) and 872 (15.5%),
respectively (Table II).

Bites occurred on a lower limb in 4 642 (82.3%) cases, and an upper
limb in 747 (13.3%) cases. Less common sites were the trunk in 107
(1.9%), face 113 (2%), and other parts of the body such as the neck or
buttock in 30 (0.5%) cases.

Of the 5 639 cases, 2 596 (46%) were referred from other health
care centres (mostly rural), while 3 043 (54%) were admitted directly to
our hospital. All the referred cases received tetanus toxoid before
admission to this hospital. Some cases also received antibiotic
treatment and antivenoms (AVs). The total numbers of snakebite cases per
year and snakebite mortality from 1999 to 2008 are shown in Table III.
The number of snakebite cases per 1 000 admissions per year remained
between 8.45 and 13.31 during 1999-2008, and the proportional mortality
rate due to snake bite remained between 1.25 and 2.86.

Table IV shows case fatality rates from snakebite by age and sex.
Fatality rates were higher in subjects <15 years old (11.9%) and in
the 46-60-year-old age group (11.8%). The fatality rate was much higher
(8.8%) in females than males (3.7%).

In this study, 70.5% of cases were from rural areas and 29.5% from
urban areas. Snakebite mortality was higher in cases from rural areas
(6.3%) than urban areas (3.4%) (Table V).

The prognosis for snakebite cases depends on various factors in
addition to their treatment, including first aid immediately after the
bite, early initiation of appropriate treatment, and the type of
envenomation (Table VI). In this study, 3 446 snakebite cases received
first aid in the form of a tourniquet or incision over the bite, or
sucking on the bite. The mortality among those who received first aid
before coming to the hospital was less (3.1%) than among those who did
not receive first aid (9.2%.) This difference is statistically
significant ([chi square]=95.36, df=1, p<0.01).

Mortality was higher (8.4%) where the time interval between the
snakebite and initiation of treatment was >6 hours, while it was less
(4.4%) where treatment occurred within 6 hours. These findings were
statistically significant ([chi square]=29.11, df=1, p<0.01).

The type of venom could not be ascertained in 1 361 cases.
Mortality from neurotoxic venom was 8.9%, and 4.2% from vasculotoxic.
The difference in mortality from these venoms was statistically
significant (%2=21.29, df=1, p<0.01)

Discussion

In the present study, snakebite was most common (57.7%) in the
31-45-year age group, followed by the 16-30-year-old age group (27%),
these groups constituting a total of 84.7% of the total. Bites were more
frequent in males than females, the ratio being 2:1. Others have
reported similar observations. (8-12)

The 16-45-year age group is most active in various outdoor
occupations, involving males more than females. Hence males are most
prone to snakebites, as seen in this study.

Most snakebite cases (3 115-55.2%) were seen in the months of July
to September, which coincides with the rainy season in this region,
followed by 1 210 (21.5%) cases during October to December. During the
rainy season, rainwater floods their burrows and snakes then try to take
shelter near human dwellings, which increases the chances of snakes
feeling threatened or startled or provoked by human beings, and biting
them in defence. The distribution of snakebite cases in different
quarters of the year was uneven, and was statistically significant ([chi
square] for goodness of fit=2960, df=3, p<0.001) and similar to other
studies. (7,9,13,14)

In this study, most bites (4 642-82.3%) were on a lower limb, and
on an upper limb in 747 (13.3%) cases. When farm workers are in the
fields, cutting grass, etc., their lower limbs, hands and fingers are
closest to ground level. Consequently, snake bites are more common on
the lower and upper extremities. (8) External factors that are not in
control of the hospitals, which increase the chances of mortality in
admitted cases, include not receiving first aid, unavailability of AV at
health centres in rural areas, no transport facilities, and lack of
public awareness about the urgency of treatment. Hence, during the study
period, snakebite cases per 1 000 admissions per year and proportional
mortality rate remained somewhat similar. Children, older people and
females are more prone to die from snakebites. In our study, the case
fatality rates were greater in subjects <15 years old (11.9%) and in
the 46-60 years age group (11.8%). The case fatality rate was much
higher (8.8%) in females than in males (3.7%), which is similar to
another report. (8) In India, owing to cultural attitudes, male health
care is often considered more important than that for females. Probably
this factor resulted in immediate treatment-seeking behaviour for males
and less importance being accorded to females.

Mortality from snakebite was higher in cases from rural areas
(6.3%) than in those from urban areas (3.4%). Dwelling conditions in
rural areas of India are more favourable for the habitation of snakes,
and most rural people are engaged in agricultural work, which leads to
more snakebites and consequent mortality.

The prognosis for snakebites depends on factors besides hospital
treatment: whether first aid is given immediately after the bite, early
initiation of appropriate treatment, and the type of venom. In this
study, mortality among those who received first aid before coming to the
hospital was lower (3.1%) than among those who did not receive first aid
(9.2%). First aid in the form of a firm bandage, immobilising the bitten
area, and incising to draw blood was applied by many patients. Mortality
was higher (8.4 %) in cases where the time interval between the bite and
initiation of treatment was more than 6 hours, and lower (4.4%) among
those who received treatment within 6 hours. Mortality from neurotoxic
snakebite was higher (8.9%) than that from vasculotoxic snakebite
(4.2%).

As a tertiary health care teaching hospital, our hospital has
facilities for managing snakebite cases. Our apparently high mortality
rate may be due to the delay in arriving at the hospital after the
snakebite, since most patients came from 80 to 100 km away, and perhaps
due to patients initially seeking treatment from traditional healers and
local practitioners.